In this document, we revised stock status assessments of D. eleginoides in research blocks 5843a_1 using CPUE analogy method, Petersen method and CASAL model, although the tagging data of current season has not been validated and not used for the present analysis. We used updated reference area size for the CPUE method. Detailed results using CASAL models in the research block are described in a separated document.
The estimated stock size in the block was 2 393, 394 and 647 tonnes in CPUE analogy method, Petersen method and R.0.1 model (vulnerable biomass in 2013), respectively. Predicted number of tag recaptures from the estimated stock sizes using the Petersen and CASAL methods was consistent with the observed number in 2013/14 season. However, these estimators were based on tags released and recaptured only at the western end of the block, as pointed out at the last WG-FSA meeting (paragraph 6.66 of SC-CAMLR-XXXII, ANNEX 6, 2013).
As for the recommendation on east and west separation of research block for management due to considerable difference of catch rates between the locations and concentration of effort in the west during the last WG-SAM meeting (para. 3.37 of WG-SAM-2014 report), we investigated the historical catch rates in relation to locations and depths by vessels. As a result, we found no significant differences of catch rates between east and west areas for principal vessels except one vessel which is mainly attributed to the concentration of effort in the west and the large difference of catch rates between the east and west during the latest seasons. Thus we consider that the above mentioned differences between the east and west areas were related to one specific vessel and not a general matter. As a sufficient number of sets have been conducted in the east area, it should be recognized that the area has finished its prospecting phase. Therefore, we believe that we do not need to separate the management in the area provided appropriate spread of effort over the bank for the vessel is ensured.
We propose to set the sample size at current 32 tonnes for at least 3 years, which is likely to result in sufficient tag recaptures to substantially refine the stock assessment, as well as constituting a sufficiently low risk harvest rate as suggested at the last WG-FSA meeting.